Mr Leung's pay will be cut by almost 85 per cent in his new job - but the 49-year-old banker said money had not been a consideration.
"I am more concerned about what I can do for Hong Kong than money or co-operation with the civil service," he said.
"The amount of money one can spend is limited . . . I always believe that the money you earn is not yours, but the money you spend is yours," he added, referring to an old Chinese saying.
Mr Leung will be in charge of one of Asia's most important financial centres and the world's largest foreign currency assets after Japan and China.
As Asia-Pacific chairman at JP Morgan Chase, Mr Leung earns $15 million a year. But his three-year civil service contract comes with an annual pay package of $2.45 million. Under the terms of his contract he can quit the post by giving three months' notice.
Having served the business sector for 28 years, he has no civil service experience but is confident he can work with 190,000 civil servants, even though unions expressed disappointment the post was not filled from within.
Mr Leung promised to observe the "traditional values" of the civil service, including remaining politically neutral. Being put in charge of the Education Commission, he said, had given him opportunities to build good working relations with civil servants.
Tung Chee-hwa said Mr Leung's experience in international banking was important in the increasingly fast-moving world of financial markets and Internet commerce.
Hong Kong Monetary Authority chief executive Joseph Yam Chi-kwong also said Mr Leung brought to the post a wealth of experience in both the public and private sectors.
Mr Leung said there was a good system of declaration of interests in the civil service, adding: "When a policy is formulated, it is very transparent and not decided by one man."
He said he would follow the financial principles in the Basic Law - namely, keeping expenditure within the limits of revenues in drawing up the Budget and striving to achieve a fiscal balance. "We shall also continue to push forward our economic development in a way that will benefit all sectors of the community. My aim is to provide economic opportunities for the many, not just a few," Mr Leung pledged.
And Mr Tsang's advice to Mr Leung? Keep smiling at legislators.